There exist known methods for producing three dimensional images in an electronic domain from solid physical objects. Typically, these methods involve some form of data acquisition of information relative to the exterior surfaces of the object, either by contact or non-contact means. The result is a computer generated image of the exterior surface of the object. For example, one such method involves physical contact coordinate measuring methods. This particular method can produce accurate physical part dimensions, but is deficient because it is time consuming to use due to the amount of data generated and because it cannot readily secure interior features of the object. Non-contact methods such as laser scanning are also capable of creating accurate part dimensions, but like the coordinate measuring methods are not readily capable of capturing internal part features. Interior features, such as surface geometries and structural elements cannot readily be captured by these methods and so they are of limited use.
There do exist methods and apparatus for capturing both internal and external features of a physical object. This is a desired and sought after ability both from the stand point of quality control of manufactured parts and because of the desire to be able to reverse engineer objects. Among the methods utilized for these ends are the non-destructive techniques of ultrasound imaging and computed tomography (CT). Ultrasound imaging is generally not accurate for reproducing physical measurements with the desired accuracy. While CT can produce modeling data of the desired accuracy, the equipment used to perform this type of operation or inspection is often quite expensive, with costs for the x-ray producing equipment, the housing for the equipment, the sensors for detecting the x-rays, and the computer resources necessary to operate the CT system often raising the cost to a figure in the one million dollar range. In addition, CT presents a radiation hazard and requires special facilities to use this equipment, which adds to the cost of their acquisition and use. Known methods of quality control and reverse engineering can also require substantial time investments in terms of human time and central processing unit or computer time. A need exists to reduce the time, cost, and repeatability of quality control sampling and to provide manufacturers a way to reliably and accurately reverse engineer an object.
Certain destructive techniques for capturing both internal and external features of a physical object a so exist. One of these is disclosed in commonly owned copending application Ser. No. 08/638,915 filed Apr. 25, 1996. That application discloses an effective technique which comprises the use of a shuttle which can move in a horizontal x direction and a z direction. The shuttle carries an encapsulated object to be digitized back and forth from a face mill to an area scanner. The face mill shaves a layer off of the top of the object. The shuttle then transports the object under an area scanner which scans the object and sends the data to a computer. A flag on the shuttle breaks a beam of light, signaling a computer to stop the shuttle so that the object is in alignment under the scanner. This position is referred to as the "x-home position." While the object is in the x-home position, an area scanner takes an image of the entire exposed surface area of the object. It is imperative that the object remain perfectly still during scanning. Once scanned, the shuttle and scanner are displaced on the z axis. Then the shuttle transports the object along the x-axis back toward the face mill, raises the object to a cutting position and another layer is cut from the object. This cycle may be repeated until the object is entirely delaminated.
Though this method is effective, it has certain shortcomings. The positioning of the object under the area scanner is crucial. The computer assumes that the shuttle is in precisely the same position during each successive scan, stacking successive images vertically to create the three dimensional image. Any actual variation in the x-home position results in a discontinuous stepping effect in the resulting computer model. Actual variations can arise from inconsistencies in the x-home position or from thermal expansion of the lead screw due to the heat generated while the object is being worked on or transported back and forth.
Another drawback of this method arises from the use of the area scanner. Even when the shuttle is in an accurate x-home position during successive passes, the area scanner is subject to inaccuracies inherent in the design of the scanner and its mounting and movement apparatus. The area scanner operates much like a photocopier. While the object to be scanned remains still, an imaging element is moved over the object to capture its entire image. The imaging element is normally powered by belts and slides along slots which are loosely fitted to the scanner so as to minimize friction. Such a traversing mechanism causes undesired, irregular movement of the scanner with resultant inaccuracies in image recording. Though these scanners are accurate enough for many applications, the present invention seeks to obtain higher levels of accuracy in image recording.
A final drawback of using area scanners is due to their size. Area scanners must be larger than the object being scanned. This results not only in an increased size of the entire machine, but also increases the amount of travel time expended while a part undergoes the delamination process. This drawback is further exacerbated by the extremely slow speeds that the shuttle must move while it's position is being fine tuned into an accurate x-home position.
It would be desirable to have an apparatus and method for creating three-dimensional modeling data from an object with a means of tracking the precise position of the shuttle throughout the digitizing process such that a computer can associate the images scanned with the actual positions of the object and assemble the three dimensional model accordingly.
It would also be desirable to have an apparatus and method for creating threedimensional modeling data from an object which incorporates a scanner that is firmly mounted and can record a series of successive images at an extremely high rate of speed such that the object being imaged can remain in motion under the scanner.
It would also be desirable to have an apparatus and method for creating three-dimensional modeling data from an object using a scanner which occupies relatively little space, thereby resulting in a reduced overall apparatus size and decreased object travel time.